Multiple pressure device for molding plastics



Feb. 24, 1942. F. H. sHAw 2374,279 Y,

MULTIPLE PRESSURE DEVICE FOR MOLDIG PLASTICS Fiqd Aug. 25, 1958 Figli mlm 5 A l Y 97%? 627%, W @/17 zoeggs i Patented Feb. 24, 1942 liJNi-TED STATES PATENT oFElcE I l 2,274,219 v` A. n... n. SG.. ...1.... t.

Shaw' Insulato r Company, corporation oi New Jersey Irvington, N. J., l

Application August 25, 1938, Serial No. 226,610 i 9 Claims. (Cl. A18u30) This invention relates to machines for molding plastics and more particularly to molding ma# c hines oi the type in which a heated cylinder iprovided into which a charge of plastic is suplpliedand in which a plunger operates to apply pressure to the plastic to render it iluent and to discharge it from the cylinder into the cavity oi a mold in whichuthe plastic is set or cured to form an article.

In such machines the plunger is operated by a ram and the maximum pressure which can be applied tothe Vplastic by the plunger is limited by the line pressure .of iluid which operates the ram and the ratio of the areas of the ram and the plunger.

' Theigeneral object of this invention is to provide a novel improvement in the above type of machines which is adapted to increase or multiply the pressure oi the ram, at a given line pressure, on the plastic in the cylinder of the machine.

Another object of the invention is to provide la novel improvement in the above type oi machine adapted to apply di'ii'erent pressures to the plastic in the cylinder of such machine. Thus, with a ram of a certain size operated at a given line pressure, an initial pressure may be used for compressing and rendering iiuent the molding' compound and for charging a mold therewith,4

and a higher pressure may then be applied while the .molded piece is setting or curing.

A more specic object is to provide a novel improvement in the above type of machine by means of which the ratio of the area of the ram and the effective area of the plunger in the cylin- `der may be changed without necessarily increasing the size of the ram .or reducing the loading capacity of the cylinder.

Other objects and advantages 'oi the invention will be pointed out, or will be apparent from, the following description of a specific embodiment illustrated in the accompanying drawing, in which:

Figure 1 is a view in vertical section of por-g tions of a machine embodying the invention;

, Fig. 2 is a similar view showing some of the parts in different positions;

Figs. 3 to 6 inclusive are views in perspective of an inner force plug, a locking ring, an outer force plug and a cylindershown in Figs. 1 andl 2; and

Fig. 'I is a view in elevation of a force plate.

By way of illustration only and not in limitation, I have shown my invention in a molding machine in which a cylinder and plunger means are assembled with a die to provide a mold unit posed segmental recesses 29 are .u which is placed between the platens of the machine to mold an article and removed from between the platens for the removal of the molded article from the die.

The platens of such machine are shown at l and I, said platens being cored as shown at 8 to receive suitable temperature controlling medium. The upper platen l is lowered and raised by a ram partially shown at II while the lower platen l may be stationary or may also be operated by a ram, not shown.

Thermold unit includes a die I2 to be charged with plastic 'to form an article and a pot or cylinder I3 which receives a. charge oi plastic for delivery to the die. f

The die I2 includes the bottom and top parts Il and Ii, the lpart I4 containing a vcavity I6 ywhich receives plastic through sprue Il inthe top part I5. The die parts are aligned by pins I8. Cylinder I3 contains a chamber- I9, the bottom of which contains sprue 2| which registers with sprue 22 in a pin plate 23, this sprue being aligned with sprue I8 in the die part I5. Y

Plate 23 carries pins 2l which ilt in holes in the bottom of cylinder I3, the purpose of which holes is explained hereinafter.

The means specifically illustrated for applying vdiiierent pressures to plastic in cylinder Il and for multiplying the pressure of ram II comprises a two-part plunger. theeffective area of which may be reduced. Said plunger includes the .outer tubular part or force plug 25 which has a tight sliding t in theY chamber l 9. and the inner piston or force plug 26 which has a tight sliding ilt in the outer force plug 26.

Force plug 26 has a head 2l, the ilat top of which may be engaged by upper platen l, said head having two diametrically opposed, segmental projections or ngers 28 on the underside thereof. Said projections are of the saxne size and shape. Between such projections two opiormed, also of the same size and shape. Y

Interposed between head 2l and the sleeve piston 25 is a locking ring 3| which has two projections 29a shaped to fit the recesses 29 on head 2l an'd between which are formed two recesses 28a shapedto receive projections 28 on head 21.

Ring 3|, which is of greater diameter than chamber I9, may ilt in an enlarged opening 32 in the top oi cylinder I3. At opposite sides ci this opening, the top of the cylinder is cut away, as shown at 3l, Fig. 6, to provide two openings for tapered lugs 34 formed on ring 3l, and to provide clearance for swinging a handle 38 on the ring.

In the opposite walls oi opening 32 tapered slots 38 are formed to receive lugs 34 on ring 3|. Thus, a bayonet joint is provided between the locking ring 3| and cylinder I3.

In operation, the parts oi die I2 are assembled and the pin plate 23 and cylinder I3 brought together and mounted on the die with the sprues 2|, 24.A I1 in line. Suitable means, not shown, may be provided for holding the die I2 in registry with pin plate 23 and pins I8 may be mounted in pin plate 23 to hold the plate and die in alignment.

The inner force plug 28 and locking ring 3| may now be assembled with projections 28 on the force plug engaging and exactly overlying pro- Jections 29a on the locking ring.

Molding compound is now charged into chamber I3 in a quantity in excess of that necessary to lill cavity I6, so that hydrostatic pressure may be maintained on the mold charge during the setting or curing period.

The outer force plug 25 is now placed in the chamber I3, and the force plug 26 and locking ring 3| assembled as a unit therewith. The ring `3| is centered on force plug 25 by a boss 25a on force plug 25 which ts in a recess in the underside of said ring. See Figs. 1 and 5. Ring 3| is placed in such angular position that lugs 34 and handle 35 line upvwith recesses 33 in cylinder I3.

Platen 1 is now forced down by ram II into engagement with. head 21 of inner force plug 26 and the pressure on the platen continued. Steam or other heating medium is circulated through platens 1 and 8 to heat the mold unit and thus heat the molding material in chamber I3. As the powder is heated and compressed, it becomes uent and is forced through the sprues 2|, 22, I8 into the heated die cavity I6.

Such discharge of the plastic from chamber I I3 results from the joint downward movement of inner and outer force plugs 26 and 25, the. pressure of ram on head 21 being transmitted through projections 28, 29a and ring 3| to the outer force plug 25. In this operation, a certain pressure is applied to the plastic, depending upon the line pressure acting on ram and the ratio of the area of the ram to the total area of the outer and inner force plugs, that is, the total area of the plunger comprising the two force plugs.

When the outer force plugreaches the bottom of its stroke, the pressure of ram II on platen 1 and on the inner 'force plug 21 is released and the locking ring 3| rotated 90 degrees by handle to engage lugs 34 thereon with slots 36 v(see Fig. 2). This locks the outer force plug 25 in lowermost position. At this time force plug 26 will be held up by the remaining plastic in cylinder I9 below this force plug. Force plug 26 should now be placed in such angular position that its projections 28 register with recesses 28a in ring 3|.

Pressure is again applied to head 21 of plug 26 by ram I and platen 1 to resume the application of pressure on the plastic preferably at a much greater pressure per square inch on the plastic than exerted jointly by j force plugs 26 and 28. Force plug 26 is prevented rom rising at this time by locking ring 3l.

The resumed pressure may serve to discharge additional plastic into the die and to further compact the plastic in the die cavity under the together.

pressure of the ram multiplied by the inner force plug 26. Or such increased hydrostatic pressure may be applied only during the period in which the molded piece cures or hardens under heat supplied by the platens 1 and 8.

Upon completion of the molding operation, the mold unit is removed from between the platens 1l and 8, broken down and the article removed from the die. The pin plate and pins are disengaged from cylinder I3 and after removal of force plug 28 and locking ring 3l, the outer force plug 25 which iits tightly in chamber I3 is driven out of the chamber by means of a force plate 31. This force plate has pins 33 mounted therein which are inserted through the openings in the bottom of cylinder I3 to engage the bottom of force plug 25 to drive it out of cylinder I3.

It will be apparent from the foregoing and from the drawing that I have provided novel means for accomplishing ,the objects hereinabove set forth. With a ram'll of given size and a given line pressure, an initial pressure may be applied to the plastic in cylinder I3 in proportion to the ratio oi the area of ram II to the total areas of force plugs 25 and 26. 'I'he ram pressure may then be multiplied or increased on the plastic in cylinder I3 by the operation of inner force plug 26 only.

For example, with ram having a diameter oi 6 inches, a line pressure of 2000 pounds per square inch, and the total plunger diameter 3 inches, the initial pressure on the plastic will be approximately 8000 pounds per square inch. With an inner force plug of 1 inch in diameter, said plug when operated alone will apply a pressure to the plastic in cylinder I3 of approximately 72,000 pounds per square inch. This greatly increased pressure is obtained without reducing the loading or charging capacity of chamber I3 in cylinder I3 and without changing the size of ram II. In other words, the ratio of ram area to the plunger area is increased by reducing the effective plunger area.

It will be understood that the effective area oi the die cavity should not exceed that of inner force plug 26 unless the parts I4 and I5 0i the die are clamped or locked or otherwise held Special clamping or locking means may be provided for this purpose but, being corn-v mon in the art, have not been illustrated.

The invention is of particular utility in molding so-called impact materials, that is, phenol-formaldehyde resins loaded with canvas stock or filler. In molding articles from such materials, it is especially advantageous to employ a certain initial pressure for charging the mold cavity and a very high pressure duringthe cure, as heretofore described.

However. the invention may be employed in molding other types of plastics and may be embodied in machines diiering in construction from that shown in the drawing withoutdeparting from the scope of the appended claims. For example, the invention may be employed in machines in which the die members, cylinder and plunger are permanently mounted and the die members are operated automatically.

The invention also may be used in a manner different from that described above. For example, in cases where a relatively small cavity die is employed, force plug 25 may be locked in position and the molding compound placed inside the force plug to be acted on only by the inner force plug 28 to charge the die and apply hydrostatic pressure during the setting or curing period. i

It also will be apparent that force plugs 25 and 2E may be varied in internal and external diameters respectively to suit different operating requirements.

Other changes and variations in the details of construction and mode of operation may be made without departing from the scope of the claims.

Having described my invention, what I claim is:

A1. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, and means for applying different degrees of pressure to plastic in said cylinder comprising a force plug fitting in said chamber, and a second force plug fitting in and movable relative to said rst-named force plug, and means for moving said force plugs together and for thereafter moving said second force plug alone toward the discharge end of said chamber to charge said die with plastic.

2. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, a tubular force plug fitting in said chamber, a second force plug fitting in and movable relative to said tubular force plug, means for holding said tubular force plug and said cylinder in relatively xed positions during movement of said second force plug, and means for effecting such movement' of said second force plug to discharge plastic from said chamber into said die.

3. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, and means for4 applying pressure to plastic in said cylinder comprising a force plug in said chamber, a second force plug within and movable relative to the rst-named force plug, and means for moving said force plugs together in the same direction and for moving said second force plug relative to the rst-named force plug after saidk rst-named force plug ha reached the end of its pressure stroke.

4. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, and means for applying pressure to plastic in said cylinder comprising a ram, plunger means comprising a force plug and a second force plug within and movable relative to said rst named force plug, means for transmitting pressure from said ram to-move said force plugs together in the same direction to apply a certain pressure to said plastic, and

, means for transmitting pressure from said ram to said inner force plug` only, to apply an increased pressure to said plastic.

5'. A machine for molding plastics vcomprising a die, a cylinder containing a chamber communicating with said die forv charging said die with plastic, and means for applying pressure to plastic in said cylinder comprising a ram, plunger means comprising a force plug and a second force plug within and movable relative to said first named force plug, means for transmitting pressure from said ram to move said force plugs together in the same direction to apply a certain pressure to said plastic, means for transmitting pressure from said ram to said inner force plug only, to apply an increased pressure to said plastic, and means for holding the rst-named force plug and said cylinder in relatively fixed positions during movement of said inner force plug.

6'. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, a ram, and plunger means for applying the force of said ram rst to the entire cross-sectional area of said chamber and then to an area in said chamber less than the entire cross-sectional area of said chamber to multiply the pressure of said ram rst applied on the plastic in said chamber.

7. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, and means for applying pressure to plastic in said chamber comprising an outer force plug tting in said chamber, an inner force plug fitting in and movable relative to said outer force plug, means for applying pressure to said inner force plug, means including a ring for transmitting such pressure to the outer force plug to move said force plugs together in the same direction, and means for locking said ring and said cylinder ltogether to hold said outer force plug in fixed position in said chamber while pressure is applied only to said inner force plus.

8. A machine for molding plastics comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic. and means for applying pressure to plastic in said chamber comprising an outer force plug fitting in said chamber, an inner force plug iitting in and movable relative to said outer force plug, means for applying pressure to said inner force plug, means including a ring for transmitting such pressure to the outer force plug to movti said force plugs together in the same direction, means for locking said ring and said cylinder together to hold said outer force plug in xed position in said chamber while pressure is applied to said inner force plug, and means for removing the outer force plug from said chamber.

9. A machine for molding plastics, comprising a die, a cylinder containing a chamber communicating with said die for charging said die with plastic, and means for applying pressure to the plastic in said cylinder comprising a tubular plunger, an inner plunger tting within and movable relative to said tubular plunger, means for holding said inner plunger retracted within said tubular plunger, and for moving said plungers together as a unit while the inner plunger is so retracted, and for moving said inner plunger relative to said tubular plunger.

FRANK H. SHAW. 

